In modern communication systems, communication connections, particularly real time connections, e.g., for voice, video and/or multimedia communication, are increasingly also by packet-oriented communication networks such as local area networks or wide area networks. For this purpose, transmission protocols from the TCP/IP (Transmission Control Protocol/Internet Protocol) family of protocols are used. A communication connection, for example for voice, video and/or multimedia communication transmitted by the Internet protocol, referred to in the following as IP, is also frequently called a VoIP (Voice/Video over Internet Protocol) connection.
VoIP connections are frequently carried out via public wide area networks such as the Internet, where network nodes participating in the transmission can in principle access the IP data packets transmitted within the framework of the VoIP communication connections. To nevertheless guarantee confidentiality of VoIP communication connections, VoIP communication data streams can be transmitted encrypted.
The IPSec (Internet Protocol Security) protocol is normally used for the transmission of IP-based communication data streams, i.e., those present as a sequence of IP data packets. By this IPSec protocol, each IP data packet to be transmitted within the context of a secure communication connection is individually encrypted and the encrypted IP data packet is transmitted.
The encryption of a VoIP data packet, however, requires a relatively high computing effort. As a rule, the maximum number of VoIP packets that can be encrypted per time unit by a transmission assembly is limited by its available processor power. In practice, the number of encrypted VoIP connections that can be carried in parallel via a transmission assembly is substantially lower than the corresponding number of unencrypted VoIP connections, because of the high encryption cost. For example, tests have shown that a typical transmission group designed for 120 unencrypted parallel VoIP connections can only encrypt 10 VoIP connections in parallel.